Actuators of the type comprising a single-action jack with springs for returning to a preferred position should the supply to the working chamber cease are already known. The energy accumulating in the springs which are compressed under the supply pressure should be sufficient to perform this movement of the pistons and rotate the control spindle.
Usually, the springs bear against the pistons at one end and against the cylinder heads or a fixed part, at the other. If shock absorbers are provided, they are arranged in the same way. In the preferred position, the pistons are located closest to one another. Between the pistons is the working chamber. The supply of pressurised fluid to the working chamber moves the pistons apart counter the force of the springs, thereby compressing them. In the event of an interruption to the main supply causing a drop in pressure in the working chamber, the energy accumulated in the springs pushes the pistons back towards the preferred position.
Owing to the fact that the compression of the springs takes place between the pistons and the cylinder heads of the fixed jack, the entire arrangement is relatively bulky. In order to fix the cylinder heads to the bodies of the jack, very long screws are needed. Moreover, as the springs bear on a fixed component at one end and on a movable component at the other, only some of the energy is recovered.
The aim of the invention is to improve the construction of an actuator of the type comprising a jack.